Sherlock and the Chamber of Secrets
by Willow Jade Flower
Summary: Wish I could've thought of a better title. Anywho, you know how in the second book Lockhart was the only man who applied for the DADA post? Well, Dumbledore saw his incapability and decided to hire another man who owes him a favor. In other words, Sherlock as a teacher during the mystery of the Chamber of Secrets.
1. Chapter 1

**Full Summary/Author's Note/Disclaimer: **So, I've been reading fanfiction like most obsessed fans, and I rather enjoyed the idea of Sherlock teaching at Hogwarts. Quite amusing, in fact to the point where I decided to write my own fanfic, despite my withdrawal from fanfic writing a year ago I think (btw the followers of my other fanfic, sorry, but I think the next update won't be for a while...), basically inserting Sherlock into the plot of the Chamber of Secrets and see how he interacts/influences the other characters.  
Basically, this is for entertainment purposes only, so I don't own BBC Sherlock or Harry Potter. I couldn't possibly come up with such golden lines/dialogue.  
Please refrain from flames, I prefer reason and suggestion. Please don't mention grammar mistakes, for I doubt I'd be able to spot those minor details. Please mention if there's a typo, though.  
I know that Sherlock's in the 21st century and Harry Potter's a century ago, but think of this as an AU - as an evil author I twisted time to transport HP's world into this time era, though apparently technology in Hogwarts is still stuck far back in time.  
This will hopefully take six chapters, give or take, for I doubt I'd be able to have the motivation to finish a long fic if I tried.  
Thank you ever so much for reading, don't forget to review, and enjoy!

* * *

**The Worst Deal**

"I assume you understand why I invited you here," Professor Dumbledore said, lacing his fingers together and resting his hands upon his desk. To his right, Fawkes let out a soft cry and began to preen.

The dark-haired man sitting across from him sat back comfortably in the chair, his dark coat and scarf draped elegantly over its back, his blue-gray eyes gazing intently at the headmaster. "My debt."

Dumbledore nodded. "Once again, the position for the Defense Against the Dark Arts teacher is available. However, only one person applied due to the... unfortunate fates of the previous teachers, and I -"

"Found Gilderoy Lockhart unqualified, and now you're appealing to me to take up the position as the way of repaying my debt. No."

Dumbledore blinked at Sherlock Holmes, and then peered at him closely through his half-moon spectacles. "Might I ask...?"

"How I knew that, or why I won't take the offer?"

"Both, if you don't mind answering."

"I met Gilderoy not too long ago at his book signings, as I was interested in how a man who doesn't leave his home without his hair in perfect condition was capable of dealing with certain creatures, and was appalled at his inability to answer simple questions about said creatures. Thus I deemed him a fraud.

"I could smell his distinct cologne once I entered this room, therefore he must had held a meeting with you not too long before you called me here. He wouldn't had met with you for a reason other than applying for the position you just mentioned, for he would rather be in front of the press or his mirror.

"As he had been reading the Daily Prophet, which I deduced from the streaked stains upon his fingers from when I shook his hand, for hesigns in such a way that his skin wouldn't be marked by the ink, therefore they must had come from clutching a newspaper - far too careful about his appearance - where I noticed beforehand your ad, which had the noted job description. He read the newspaper, saw said ad, and came for an interview.

"As I said before, he is clearly unqualified due to his lack of knowledge or sense. As you said, only one person would apply because of the unfortunate fates of the previous teachers - as the man shows an oversized ego and idiocity, it's so far so obvious that he would be the only one to apply.

"I owe you for assisting me in the elimination of Moriarty's network, not to mention the man himself, and so after a couple of months without word and a few of weeks before the usual start of school, you invite me to your office. This means you have found a way for me to repay my debt, and that is for me to fill this position."

There was a moment of silence as Sherlock finished explaining his deductions and reasoning. Dumbledore studied the man carefully. He remembered teaching the former Ravenclaw - at Hogwarts Sherlock had an incredible intellect and thirst for knowledge, always reading book after book in the library, even venturing into the Restricted Section for them. However, the boy was friendless, easily bored, often sullen, and sometimes slacking off on homework. The Holmes family was an old wizarding family, and after growing up in the magical world, Sherlock found the Muggle world far more interesting, with crimes that bore oddities Muggles couldn't solve themselves. After seeking help from his squib older brother Mycroft (who, with a strong position in the Muggle government, was an invaluable link and help to the Ministry of Magic), he put away his wand and lived among Muggles as their only consulting detective, solving their puzzles and learning their technology, for their sciences were constantly expanding with new things to learn and experiment, despite the frequent stupid Muggle.

After many years of teaching, then adopting the post as headmaster, Dumbledore hadn't heard a word of the intelligent wizard who left for the Muggle world until he showed up at his doorstep, having recently faked his death and desperate to protect the ones he cared for. Three years later with great success, they agreed that Sherlock would have to do Dumbledore a favor in the future.

And now, Dumbledore still found himself impressed by the abilities of Sherlock's mind - all the more reason to hope the man would agree.

"Why are you reluctant to accept the post?" Dumbledore said quietly, seeing that Sherlock had fallen silent.

Sherlock huffed. "For one, I would rather be helping the slow-witted officers of Scotland Yard than attempting to teach mindless children how to tell a hex from a jinx. I doubt my patience would last. Thank you very much, I'll take the next favor."

He gave Dumbledore a false, tight-lipped smile as he prepared to rise.

"So you say. However I strongly believe you would be able to pass on more information than Mr. Lockhart," Dumbledore said.

"I'm flattered."

"Sherlock, I must insist. There is no other favor I would rather you take."

Sherlock slowly let out a breath and squinted at Dumbledore as if determined to deduce him further. "Are you sure?"

"Harry Potter will be returning for his second year at Hogwarts - the boy whom Voldemort is after. Last year Harry was nearly killed by him - I have no doubt Voldemort will attempt at the deed again. I may need your help protecting him and keeping an eye on suspicious events," Dumbledore said gravely. "And yes, I am absolutely sure."

There was silence in the room. Finally, Sherlock said, "Can I bring John?"

"Who?"

"John, my John - erm, my blogger - um, friend." Sherlock cleared his throat and looked over to the side awkwardly. "See, he didn't take it quite well that I faked my death and didn't say so for three years, and won't leave me alone for longer than an hour. I only managed to Apparate at your message from the flat because he was out getting milk. I greatly doubt I can vanish - again - for a school year without him never letting me hear the end of it."

"Is he a Muggle?"

"Yes."

Dumbledore was quiet for a few moments. "I suppose you won't come otherwise."

"Nope."

"I also suppose that you'll come up with a loophole in the rules and bring him anyway."

Sherlock gave him a _duh_ look.

"I hope I'll be seeing you on the first of September at Hogwarts, then," Dumbledore said, rising and extending a hand.

It was only after a few moments of Sherlock's intense concentration on the decision before he shook Dumbledore's hand to close the deal. "One more thing, though" he said with a smirk. "I am _not_ wearing robes."


	2. Chapter 2

**Author's Note/Disclaimer: **Rest of the story will be in Harry's POV like in the books. Don't own HP or SH. Many thanks to those who followed/favorited.

* * *

**Sherlock Holmes**

Harry and Ron sat down at the Gryffindor table next to Hermione. There was a slight stiffness in the way she said "Morning," which told Harry that she was still disapproving of the way they had arrived. Neville Longbottom, on the other hand, greeted them cheerfully.

"You weren't at the feast last night, so do you know about the new Defense Against the Dark Arts teacher yet?" he asked, nodded towards the teachers' table. "Professor Holmes."

Harry turned his head and scanned the table, his eyes settling on the unfamiliar face of the new professor. He looked clearly uncomfortable and was picking at his food. His dark curls were unbothered by a hat, and his gaze would focus on another teacher or out towards the students as if he were studying them.

He turned his head back as Neville was saying, "Mail's due any minute..."

* * *

It was before Herbology that Harry saw Professor Holmes for the second time. He was accompanied by Professor Sprout, whose arms were full of bandages. Her voice traveled over towards the class.

"Why don't you ask Professor Snape? He's more likely to have what you need," she was saying. "This wouldn't happen to be another incident like the one where your office nearly exploded before the Great Feast, would it?"

"That was an experiment," Professor Holmes replied a bit stiffly, "that I'll be sure not to repeat."

"Care to explain why there were eyeballs in -"

"I said it was an experiment! ...Whether a cauldron would be the same as the microwave, that is."

"A what now?"

"Never mind, I see you have a class to get to - I'll see if Professor Snape has them."

"Try not to rile him up again."

"It was just an observation!"

"Most people wouldn't say it out loud."

"He asked - oh nevermind, I better go." He strode away in a similar fashion as Snape, muttering something about "stubborn old man" and "good coat".

Ron was staring after him - most of the class was, having overheard the conversation. "Eyeballs?" he half whimpered.

* * *

By the time the Defense Against the Dark Arts class came around, Harry's curiosity about the new professor had heightened after hearing about the highly observant man through rumors that rippled through the hallways. When he entered the classroom, like the other second years, he scurried quickly to his seat. Professor Holmes hadn't entered the classroom, though on the chair behind his desk there was a coat, a jacket, and a blue scarf draped over the back of the chair.

Then, the doors opened almost ominously, and Professor Holmes walked in, reminding Harry oddly of Snape.

"This class," he announced, "is to prepare you against the dangers of magical origin. This includes dangerous creatures and spells that could deal you harm. In order for you to completely understand the basics of how to defend yourself, I will need your full and undivided concentration. This means no talking, no trouble-making, or time-wasting, or any other ways children get themselves into these days. These I certainly won't tolerate and will not hesitate to punish you for it. Another thing is no stupid questions. My patience has already been tested this morning. Now, for your first class, you will open your book to the first chapter and read it thoroughly. No talking above a whisper, no asking meaningless questions unless it is an emergency, I'll be in my mind palace."

After this abrupt announcement, he spun on his heel and sat down in his chair, proceeding to stare at the wall in a strange concentration. The rest of the class seemed slightly baffled, but wisely didn't ask any questions and began was much fumbling for the books and flipping of pages. Harry peered over at Professor Holmes, whose hands were in front of him and twitching as if flipping the pages of a book as well.

"Mind palace?" muttered Ron next to him, clearly just as puzzled as Harry.

* * *

"_You _will be polishing the silver in the trophy room with Mr. Filch," said Professor McGonagall."And no magic, Weasley - elbow grease.

"And you, Potter, will be helping Professor Holmes in his office. Apparently when he heard a student got detention he asked for such assistance at once with no details. Eight o'clock sharp,both of you."

Harry had the strangest sense of doom upon hearing this, and both he and Ron slouched into the Great Hall. Eight o'clock seemed to loom closer and quicker as the afternoon melted away, and Harry's imagination started boiling with more dreadful thoughts of what the DADA professor wanted him to do. He kept recalling the conversation with Professor Sprout, and felt he wasn't quite ready to become a test subject for an experiment.

Staring up at the door to Holme's office, Harry subdued his imagination, gritted his teeth and knocked.

Silence, save for the hooting of an owl. After a few moments of awkward shuffling in front of the door, Harry heard a lazy, "Come in, Harry Potter."

Feeling even more nervous about this detention, he pushed open the door, and found himself blinking at the incredibly messy state of Holme's office. Boxes, books, and papers littered the floor, the stacks more concentrated near the walls. His desk was covered in Muggle lab equipment with his robes quite carelessly thrown over the end, nearly slipping off. A skull sat nonchalantly on the desk as well, its dark eyeholes staring blatantly at Harry. There was a short, disgruntled-looking tawny owl perched above Holme's head. The professor himself was stretched out on a couch in Muggle attire, his wand in hand, levitating an object and Transfiguring it in the air.

Harry blinked a few more times before he entered, carefully picking his way through the mess. The owl hooted again, seemingly staring down at Holmes as if ready to chide him.

"Um, sir...?"

"Yes?" Holmes murmured, clearly transfixed on whatever he was doing.

"I have... a detention with you, sir-"

"Oh, yes, first, can you pass me my phone?"

"Sir?"

"'Sir' sounds too much like Mycroft - if not in class, call me Sherlock. My phone. A device used to transfer information over a long distance, much like your system of owls. In my jacket."

Harry blinked at him, trying to digest the oddly simple request when the owl hooted sharply at Sherlock, lifted its wings, and flew past Harry towards one of the two chairs next to the messy desk, using its talons to lift the black clothing. Harry moved over, still trying not to step on any of the papers, and uncertainly looked in the jacket's pocket, finding the mobile in the front pocket. He walked back to Sherlock, who had lowered the object to the floor with magic, and gave it to his waiting hand. Still on his back, Sherlock shifted it up so that he could text.

"Sir - um, I mean, yeah, why do you have a mobile phone?" Harry asked, still confused.

"To transfer information over a long distance without moving," Sherlock replied slowly. "Next stupid question?"

Harry gaped at him for a few moments before managing to say, "You don't use your owl?"

"I greatly doubt John would let me treat him as post delivery." The owl seemed to hoot in agreement.

Harry nearly asked "John?" which would've surely given him a "I'm an idiot" label.

"Also, I have to text a Muggle - an owl would just attract attention. The morons at Scotland Yard are still asking for help despite the fact I'm clearly away teaching. I wonder if the castle has Wi-Fi..."

"Scotland Yard? Help?"

"Yes, I should probably explain, I've been living as a Muggle for the past decade as a consulting detective, but I'm now here for the year as a favor to Dumbledore." Sherlock sighed as he sent the text and sat up. "I had to recall all the spells and information that I hadn't deleted yet, for God's sake. Something better happen this year, or I will be stuck teaching nose-pickers for the entire year. Boring!" He turned towards Harry. "You're the Boy-Who-Lived, aren't you? Lived with Muggles - who clearly mistreat you, but you have no other relatives to go to, so you're stuck with them. You had sherperd's pie at dinner, as the crumbs on your robes suggest. The girl who sat across from you fancies you, but you don't share her feelings. You have a clever friend who's forcing you to read the History of Hogwarts, but you are clearly not interested."

Sherlock was cut off by the sharp hooting of the owl. "So I made a student cry, that was one time! - Not counting the ghost. I'm bored!"

The owl hooted. Harry felt slightly frightened. "Huh? But- how did you know?"

Sherlock huffed. "I didn't know, I saw. But, now's the time for your detention. I need assistance with an experiment. No, it's not dangerous."

He walked over to his desk and gestured for Harry to come. "This shouldn't take too long. Are you familiar with boomslang?"

* * *

The detention was surprisingly not as bad as Harry thought. Sherlock was rather blunt and quick to point out Harry's slowness and had the tendency to say his deductions about the second-year. As the hour passed, Harry found his amazement and discomfort slide away as he worked with the man. It was rather like Potions, only with Muggle equipment rather than the cauldron.

Harry was wondering what Sherlock was experimenting when he heard something - something quite apart from the spitting of the dying candles and Sherlock's baritone voice directing him. It was a voice of breath-taking, ice-cold venom.

_"Come...come to me...Let me rip you...let me tear you...let me kill you..."_

Harry gave a huge jump and nearly knocked a beaker over. _"What?" _he said loudly.

"I said to pass me the beaker with the green liquid," Sherlock said, holding his pipette vertically.

"No," said Harry frantically, "That voice!"

"What voice?" said Sherlock sharply.

"That - that voice that said - didn't you hear it?"

Sherlock gave him a look that answered him. He cast a glance at the clock and simply said, "That should be all. Thank you Harry." And with a nod, Harry was dismissed. Harry stumbled over to the door, a bit too dazed to watch out for the papers he was unwittingly stepping on, straining to hear the voice again. When he looked over his shoulder, Sherlock was nodding to the owl.

Outside the office as Harry was walking down the hallway, Harry didn't hear the voice again. Instead, he heard a fizzing sound, then a sharp _crack__!_ from Sherlock's office followed by Sherlock's voice. "Oh, shut up, John."


	3. Chapter 3

**Disclaimer: **I don't own HP or SH, thanks for reading.

* * *

**The Writing on the Wall**

Something was shining on the wall ahead. Harry, Ron, and Hermione, panting from the run following Harry's ears, approached slowly, squinting in the darkness. Foot-high words had been daubed on the wall between two windows, shimmering in the light cast by the flaming torches.

THE CHAMBER OF SECRETS HAS BEEN OPENED, ENEMIES OF THE HEIR, BEWARE.

There underneath it was Mrs. Norris, the caretaker's cat, hung by her tail from the torch bracket.

* * *

Upon hurrying onto the scene, Sherlock's face, illuminated by the torch light, had lit up with delight as if Christmas had come early. Completely ignoring Mr. Filch's screeching and the three frightened second-years, he strode right up to the wall and peered at the words. Touching the still-wet line of a T, he brought his red-stained finger to his nose to sniff at it. He pulled out a magnifying glass and bent slightly to look at the words more carefully. Sherlock looked down at the large puddle of water one foot was standing in thoughtfully.

_"Argus!" _Dumbledore's voice cut Mr. Filch's accusation against Harry short as he, followed by a number of other teachers, swept past Harry, Ron, and Hermione to detach Mrs. Norris from the bracket.

"Yes, please do shut up, your babbling is hardly worth listening to," muttered Sherlock as he straightened from the wall. "My office is nearest, feel free to take the cat there. It's just upstairs."

"Thank you, Sherlock. Come with me, Argus. You too, Mr. Potter, Mr. Weasley, Miss Granger," said Dumbledore.

The silent crowd parted to let them pass. Professor McGonagall, Snape, and Sherlock hurried after Dumbledore as well.

As they entered Sherlock's darkened office, there was an alarmed hoot from John. Sherlock used his wand to light candles and hurried forward to shove his stuff off of his desk for use. Dumbledore lay Mrs. Norris on the polished surface and began to examine her. Harry, Ron, and Hermione exchanged tense looks and sank into chairs outside the pool of candlelight, watching.

The tip of Dumbledore's long, crooked nose was barely an inch from Mrs. Norris's fur. Professor McGonagall and Sherlock were bent almost as close. Snape loomed behind them, half in shadow,wearing almost peculiar expression. Filch was slumped in a chair by the desk, unable to look at Mrs. Norris, his face in his hands as he sobbed.

At last Dumbledore straightened up. "She's not dead, Argus," he said softly. "She's been Petrified. But how, I cannot say..."

"Ask _him!"_ shrieked Filch, turning his blotched and tearstained face to Harry. "You saw what he wrote on the wall! He knows I'm a Squib!"

"I never _touched_ Mrs. Norris!" said Harry loudly, uncomfortably aware of everyone looking at him. Dumbledore and Sherlock were both giving him a searching look.

"If I might speak, Headmaster," said Snape from the shadows, "Potter and his friends may have simply been in the wrong place at the wrong time. But we do have a set of suspicious circumstances here. Why was he in the upstairs corridor at all?"

Harry's sense of foreboding increased as he and his friends quickly launched into explanations, then further interrogated by Snape, whose nasty smile continued to widen.

"I suggest, Headmaster, that Potter is not being entirely truthful," he said.

"Of course he's not, it's obvious," said Sherlock, and Harry's heart dropped. "It's just as obvious that none of them had a hand in Mrs. Norris's petrification or the words on the wall."

Practically everyone in the world stared at him in confusion, save for Dumbledore, who had a knowing gleam in his eye. "Please explain, Sherlock."

"The writing on the wall," he said, "It's about four feet from the ground, not to mention the handwriting says that a student wrote it. It's red paint that hasn't dried yet, and to write all those words one would need a bucket full. The words were written with a finger, which you can tell by the way the paint was smeared, not streaked like from paintbrush, and the person who wrote them needs their fingernails clipped. There are scratches on the wall from the nail behind the paint. None of these three students have red paint on their robes, not even drops of the sleeves. If they may all show their hands -" which they all did quickly at the indirect command "- you can see there is no sign of red paint underneath the fingernails or around the cuticles, which would be a sure sign of hasty cleaning of the paint. Since the paint still hasn't dried, the writer had left a little before this trio arrived at the scene, which means he or she would have little time to clean up. The person who wrote the words also hung the cat on the bracket - you can see the paint flecks in its fur. And I wouldn't be surprised if the water on the floor had to do with the petrification. According to the smell of it, it came from the bathroom."

When Sherlock finished speaking, Harry felt greatly relieved. Snape looked as if Sherlock had forced one of his experiments down his throat.

"Then who did it?" demanded Filch, his reddened eyes looking ready to pop from their sockets.

"A first, second, or third-year student or a short Dark wizard, most likely a female according to the handwriting," murmured Sherlock thoughtfully. "Dark wizard being more likely since advanced Dark magic can be used to Petrify. Other than that, I need more data."

Filch remained furious, possibly by the incredibly calm and matter-of-fact way Sherlock said it. "My cat has been _Petrified!_" he shrieked.

"Marvelous deduction, too bad it's already been said. Do try to keep up," Sherlock replied dryly.

"We will be able to cure her, Argus," said Dumbledore patiently, casting a quick warning look towards Sherlock. "Professor Sprout recently managed to procure some Mandrakes. As soon as they have reached their full size, I will have a potion that will revive Mrs. Norris." Dumbledore looked over towards Harry, Ron, and Hermione. "You may go."

They went, as quickly as they could without actually running.


End file.
